The perimeter of the pentagon is
35y⁴ – 65x³
We let s as the length of one side of the sandbox. Since the sandbox is a pentagon, it's perimeter is given by
P = 5s
5s = 35y⁴ – 65x³
Solving for s
5s = 5(7y⁴ - 13x³)
s = 7y⁴ - 13x³
The length of one side is 7y⁴ - 13x³.
